Offshore platform with internal flowline



Nov. 19, 1968 R. D. BATES ETAL 3,411,303

OFFSHORE PLATFORM WITH INTERNAL F'LOWLINE Filed Dec. 28, 1966 y 2Sheets-Sheet l INVENTORS:

R. C. VISSER R. D. BATES BY: l THEIR AGENT NGV. 19, 1968 E E R, D. BATESETAL 3,411,303

OFFSHORE PLATFORM WITH INTERNAL FLOWLINE Filed Dec. 28, 1966 2Sheets-Sheet 2 24 nfZ'a' INVENTORSZ R. C. VISSER R. D. BATES THEIR AGENTUnited States Patent 3,411,303 OFFSHORE PLATFORM WITH INTERNAL FLOWLINERichard D. Bates, Anchorage, Alaska, and Robert C. Visser,lSan Dimas,Calif., assignors to Shell Oil Company, New York, N.Y., a corporation ofDelaware Filed Dec. 28, 1966, Ser. No. 605,422

9 Claims. (Cl. 61-46) l ABSTRACT OF THE DISCLOSURE An offshore platformprovided with at least one internal passage in the structural members ofthe platform for receiving and protecting a owline from ice floes, watercurrent, debris and the like. The passage, which may be a separate tubewithin a leg and cross-bracing of the platform, serves to guide theilowline as it is pulled through the passage from the ocean floor up tothe surface of the platform. v

This invention relates to offshore installations of the type having aplatform above the surface of the water and more particularly to aninstallation of this type adapted to protect a flowline extending fromthe water floor up to the platform from water currents, debris, ice oes,water craft and the like.

The development of offshore oil and gas wells frequently necessitatesthe use of offshore installations or socalled platforms." Theseinstallations are used, for example, for drilling and subsequently forproducing a well or wells. Accordingly, it is often desirable to provideone r more owlines from the platform to a remote point, e.g., to shoreor another platform. The owlines serve many purposes, the most commonbeing to carry oif the output of oil or gas from a well.

The present practice for handling the ilowlines is to provide a verticalowline riser along the side of the installation extending to the waterfloor and connect it to a flowline which extends along the oor to thedesired destination. This practice leaves the flowline riser exposed andfrequently requires divers to make underwater riserto-owlike connectionsand also to connect the riser to the platform.

Since the riser is exposed, it is subject to damage from water currents,debris, ice oes and the like and, if the riser extends beyond theperipheryof the installation, it is subject to being rammed by watercraft attending the installation. Thus, present practice often requiresthat the riser be made of heavier gauge than the flowline, that it beattached to the installation, that spoilers may belemployed 'to break upeddy currents caused by the water, and even that the riser be encased ina special casing.

The problem is particularly prevalent where large ice floes and rapidcurrents are encountered, e.g., at the Cook Inlet in Alaska which isicebound much of the year and, due to severe tides, experiencescontinually cycling ice floes into and out of the inlet.

Accordingly, there is a need for a simple, compact arrangement forconnecting an underwater flowline to a platform located above the watersurface which fully protects the owline from the above-mentioned edects.It is to this end that the present invention is directed by eliminatingthe need for a owline riser mounted alongside the installation.

In general, the invention provides an offshore installation supported onthe floor of a body of water and having an internal passage forreceiving and protecting a flowline extending from the Water oor to thewater surface. The passage is adapted to communicate with the body ofwater near the water floor and extends internally of the installation upto or beyond the water surface so that a Fice owline positioned alongthe oor of the body of water may be pulled through the passage and up tothe surface.

It is therefore a primary object of this invention to provide anoffshore installation for protecting a iiowline extending from the oceanfloor to the platform of the offshore installation.

It is a further object to provide apparatus for protecting a owlinewhich is carried internally of the structure of the offshoreinstallation.

It is a still further object to provide apparatus which is compact andadaptable to existing installation.

Another object is to provide apparatus which permits the owline to bepulled from the ocean floor up to the platform by means of a drawline.

Still another object is to provide an apparatus which is adaptable toany type of offshore installation.

These and other objects will become apparent from a reading of thefollowing detailed description taken in conjunction with theaccompanying drawings in which:

FIGURE 1 is an elevational view of a typical offshore installation towhich the present invention is adapted with a ilowline installed;

FIGURE 2 is an elevational view of the same offshore installation with aowline about to be installed;

FIGURE 3 is an elevation of the lower portion of the offshoreinstallation partially cut away to show the flowline receiving tubes ofthe present invention;

FIGURE 4 is a cross-section of one of the legs of the offshoreinstallation taken along line 4-4 of FIGURE 3; and,

FIGURE 5 is an elevational view taken in perspective of a modifiedoifshore installation to which the present invention is adapted.

Referring to FIGURE 1, an offshore installation to which the presentinvention is adapted is indicated generally at 10. As shown, theinstallation comprises a plurality of support means or legs 11 anchoredin the lioor 12 of a body of water `13. A working platform 14 issupported by the legs 11 and is arranged to remain above the surface 15of the body of Water 13. The platform 14 may be single or multi-deckedand normally carries a complement of production equipment necessarytoproduce oil or gas from wells drilled, as through the legs 11. Asshown, this equipment may include crew `quarters 16, crane 17 andprocessing equipment 18 which may be surge tanks, separators and thelike.

As may be'best seen in FIGURE 4, each leg includes a plurality ofconductor tubes 18 which extend the length of the leg and serve as aconductor for drilling operations or for diving anchor pillings tosecure the leg to the floor 12. For example, as shown in FIGURE 1, theoff-take of a well 19 (previously drilled through one of the conductors18) is produced through casing 20 positioned in a conductor 18. Duringthe drilling operation a suitable drilling rig (not shown) is located onthe platform 14 to perform the drilling operations through theconductors 18. After the drilling is completed the rig may bedisassembled and removed. As shown in FIGURE 4 each leg 11 is providedwith, e.g., eight conductors, which would thereby give the entireinstallation a 32-well capability. The present invention, however, isnot meant to be limited to a platform in which wells are drilled throughthe platform legs. The invention could be adapted to a platform in whichwells are drilled through individual conductors elsewhere on thestructure.

The legs 11 are interconnected by tubular cross-bracing including ahorizontal cross-bracing member 21 and an X-shaped cross-bracing member22 or so-called diagonals between each pair of legs so that the legs andcrossbracing from a structure of closed configuration.

The detail of the supports 21 and 22 and the legs 11 are best shown inFIGURE 3 which illustrates these members partially cutaway to reveal thetubular construction. Each leg of the X-shaped member 22 may carry aflowline receiving tube; one extending axially through the right leg (asviewed) indicated by 23 and the other indicated by 24 although it is notnecessary to have both. The flowline receiving tubes 23 and 24 arepreferably secured during fabrication to the inner walls of the member22 by straps 25 or other suitable means. Similarly, the receiving tubesare suitably secured within the legs 11 and extend to the platform 14 asshown in FIGURE l in which ilowline receiving tube 23 is represented bydotted lines. The lower end `of tube 23 extends through the left leg 11and terminates with a flanged connector 26. Although the lower end oftube 23 is shown as being canted slightly downward, it may be desirableto curve the lower end so that it terminates in a substantiallyhorizontal position. Accordingly, when the lower end of the tube is socurved, it will be apparent that the flanged connector 26 will also bedisposed horizontally rather than as shown.

The tube 23 is attached and sealed to the leg 11 at 27, for example bywelding, to secure the tube and prevent sea Water from entering the legaround the tube 23. Thus, it will be seen that the ilowline receivingtube 23 establishes a passage within the structure of the installationfrom a point near the lioor 12 of the body of water 13 to the platform14. In addition, other owline receiving tubes may be installed withinthe leg and cross-bracing of the offshore installation, e.g., the owlinereceiving tube 24 which is positioned in the other leg of the X-shapedcrossbracing member 22. Accordingly, the number of owline receivingtubes employed will be dictated by the flowline requirements of eachoffshore installation. When the relative size of the flowline receivingtube and the cross-brac ing members permit, more than one tlowlinereceiving tube can be mounted in parallel. As shown for example, theowline receiving tube 23 is sufficiently smaller than the internaldiameter of the X-shaped member 22 so that several tubes could bepositioned to follow substantially the same path as tube 23.

Although the offshore installation disclosed is a 4-legged structure, itis contemplated that the subject invention could be practiced with otherstructure, e.g., single-leg, 3- leg, 6-leg or 8-leg platforms. In FIGURE5, a single-leg offshore installation is shown incorporating the presentinvention. The installation comprises a platform 32 carried by a mainsupport leg 39 and a plurality of downwardly sloping support members 29.The leg 39 and one of the members 29 carry a flowline receiving tube forsupporting and protecting a owline 31. One end of tube 25 extendsthrough the wall of the support member 29 in the vicinity of the wateroor and the other end terminates at the platform 31 where it may beconnected to processing equipment to handle the produced gas or oil fromwells (not shown) drilled through the leg 39. As mentioned above withreference to the preferred embodiment of FIGURES l-4, the single-legstructure of FIGURE 5 may utilize more than one flowline receiving tube.Each member 29 may be fitted with a tube or a plurality of tubes ma'y beclustered within each member 29.

Referring again to FIGURES 1 4, it will be seen that the flowlinereceiving tube 23 provides a protective path for a owline 33 and extendsfrom a point near the oor 12 of the body of water 13, through theinstallation 10 to the surface of platform 14. The flowline 33 is pulledthrough the tube 23 after the installation 10l is set up by means of adrawline 34 (see FIGURES 2 and 3) secured to'the end of flowline 33 witha suitable connector. Preferably, the drawline 34 is strung through thetube 23 prior to setting up the installation 10.

One end of thel drawing 34 is secured to suitable hoisting means, e.g.,a winch 35, as shown in FIGURE 2 and the other end may be brought backup leg 11 to the platform 14 or it may be buoyed off to float in thewater for subsequent recovery.

When it is desired to install the flowline 33, the free end of thedrawline 34 is secured to the tlowline which may, for example, be laidon the floor of the body of water 13 by means of a reel-type barge 38.As best shown in FIG- URE 2, the drawline 34 is secured to the owline 33and the barge 35 proceeds away from the installation 10 as the owline 33is payed out. After sufficient flowline has been laid on the floor 12 toprevent undue bending, the winch 3S is employed to pull the tlowline 33through the flowline receiving tube 23 and up to the platform 14. As theflowline is being pulled, the barge 38 continues to pay out flowline toprovide slackor slack may be provided by laying excess owline in theform of a loop in a suicient amount to permit the flowline to pass thelength of tube 23 without bending.

In order to prevent kinking or flattening of the flowline 33 as it ispulled into place, the curvature dictated by the X-shaped cross-bracingmember 22 and the right leg 11 (a's viewed) must not be too sharp. Thus,the angle at which the cross-bracing member 22 slopes downwardly awayfrom the leg 11 should be great enough (preferably 30-60) to assure agradual curve. In addition, the size of the leg 11 will affect thecurvature. Accordingly, the angle of member 22 with :respect to leg 11and the size of leg 11 should be selected to provide at least theminimum radius of curvature permissible for a given size flowline toprevent permanent flattening of the owline.

In order to facilitate the entry of flowline 33 into the tube 23, it ispreferable to employ a flared guide 36 on the end of the tube 23. Theflared guide 36 is preferably formed with a flanged connector 37 to matewith the connector 26 on the tube 23. Thus, the guide may be fastened tothe tube 23 at any time either prior to setting up the installation 10or once the installation is set up it may be installed by employingdivers. The guide is ared outwardly to compensate for any angularitybetween the flow line 33 and the tube 23 during pulling. The guide 36may of course be formed integrally with the tube 23 or it may also beattached by other suitable means, e.g., weldlng.

When the guide 36 is installed after the drawline 34 is in place, itwill be apparent that the guide must be threaded over the drawline 34and then suitably secured to the tube 23.

A similar flared guide is also preferably employed with the embodimentdisclosed in FIGURE 5. The procedure for pulling the flowline 31 throughthe flowline receiving tube 30 is essentially the same as describedabove with reference to the preferred embodiment of FIGURES 1 4.

Up to this point the description of both embodiments has been predicatedon the use of a flowline receiving tube through which a flowline ispulled. It is contemplated, however, that the instant invention may bepracticed without the necessity of employing such a tube. When the tubeis not used the structural members of the installation 10 serve asilowline carrying means through which the flowline is pulled.

For example, in the preferred embodiment of FIG- URE l the owline couldbe pulled within the legs 11 and the cross-shaped member 22 without thetube 23. In this case it is preferable to employ a tapered probe or tip(not shown) on the pipeline so that it will pass freely through the legs11 and cross-shaped member 22 without sticking. In addition, suitabledellectors may be incorporated within the installation at criticalturning points, openings, etc., to guide the owline and prevent it frombecoming stuck. A flared guide similar to the guide 36 may be secureddirectly to the platform at the point the owline enters the installationto aid in starting the owline.

Once the owline is installed, it may be connected to any suitableequipment, e.g., the output of a well 19 as shown in FIGURE 1. Theflowline, however, may serve other purposes. It may serve to connect twooffshore installations to carry the production from one installation tothe other or as a supply line, etc. The flowline may extend to shore, toanother platform installation or to an underwater collection facility.

The above-described invention provides a fully protected path for aowline extending from the floor of a body of water to an offshoreplatform above the water surface. The invention protects the ilowlinefrom damage from ice floes, water currents, waves, surface craft anddebris and at the same time provides a compact more eicientinstallation.

Having thus described the invention what is claimed is:

1. An offshore installation positionable on the oor of a body of waterand including apparatus for supporting an underwater ilowlineconnectible to said installation and protecting it from ice, watercurrent, debris and water craft comprising:

substantially vertical hollow support means positioned on the oor ofsaid body of water and extending above the water surface;

platform means supported by the upper end of said support means abovesaid water surface;

independent downwardly sloping hollow owline carrying and containingmeans having an upper end and a lower end;

said upper end being secured t0 said support means and in opencommunication with the interior thereof; and,

said lower end terminating near the floor of and being in opencommunication with said body of water when said offshore installation isoperatively positioned on the floor of said body of water;

whereby said hollow owline carrying and containing means and said hollowsupport means define a closed path between the lower end of said owlinecarrying and containing means and the upper end of said support means.

2. An offshore installation as defined in claim 1 wherein said flowlinecarrying and containing means comprise:

iirst passage means in said owline carrying and containing means forreceiving a flowline, said rst passage means having one end incommunication with the water outside said leg means near the floor ofsaid body of water; and,

second passage means in said leg means in communication with the otherend of said rst passage means and extending to the top of said leg meansfor receiving said flowline;

whereby said rst and second passage means comprise said closed path forsaid flowline.

3. An offshore installation as defined in claim 2 wherein said hollowsupport means comprise a plurality of hollow legs.

4. An offshore installation as dened in claim 3 wherein said downwardlysloping ilowline carrying and containing means comprise a hollowcross-bracing member of said offshore installation having the upper endthereof secured to one of said legs and the lower end thereof secured toa second leg; and,

said second leg being provided with opening means in alignment with saidrst passage means to provide access through said leg to said firstpassage means;

whereby said passage means and said opening means comprise an enclosedpath for said ilowline between said opening means and said platform.

5. An offshore installation as dened in claim 4 wherein said rst andsecond passage means are formed by:

a continuous flowline receiving tube; and,

said tube extends through said opening means in said second leg.

6. An offshore installation as defined in claim 5 includlng:

hoist means positioned on said platform means and including a wiredrawline attachable to said owline for pulling said flowline throughsaid tube.

7. An offshore installation as dened in claim 6 wherein said hollowcross-bracing member slope downwardly at an angle of 30 to 60.

8. An offshore installation as dened in claim 7 wherein said angle ofsaid downwardly sloping hollow cross-bracing member and the size of saidfirst leg provide at least a minimum radius of curvature of saidflowline when pulled through said tube to prevent a substantial changein the cross-sectional shape of said flowline.

9. An offshore installation as deiined in claim 5 ino cluding:

References Cited UNITED STATES PATENTS JACOB SHAPIRO, Primary Examiner.

